In vitro ovine articular chondrocyte proliferation: experiments and modelling

This study focuses on analysis of in vitro cultures of chondrocytes from ovine articular cartilage. Isolated cells were seeded in Petri dishes, then expanded to confluence and phenotypically characterized by flow cytometry. The sigmoidal temporal profile of total counts was obtained by classic haemocytometry and corresponding cell size distributions were measured electronically using a Coulter Counter. A mathematical model recently proposed ( 1 ) was adopted for quantitative interpretation of these experimental data. The model is based on a 1‐D (that is, mass‐structured), single‐staged population balance approach capable of taking into account contact inhibition at confluence. The model’s parameters were determined by fitting measured total cell counts and size distributions. Model reliability was verified by predicting cell proliferation counts and corresponding size distributions at culture times longer than those used when tuning the model’s parameters. It was found that adoption of cell mass as the intrinsic characteristic of a growing chondrocyte population enables sigmoidal temporal profiles of total counts in the Petri dish, as well as cell size distributions at ‘balanced growth’, to be adequately predicted.     

A Monte Carlo Study of Ring Polymers in Disordered Systems

Abstract

We study the properties of ring polymers in disordered systems using a Monte Carlo algorithm. The algorithm is used to generate a ring on a two dimensional lattice, and the disorder is represented by the random dilution of the lattice. We show how the ring undergoes a cross-over from obeying self avoiding statistics at low concentrations of disorder, to behaving like a branched polymer as the concentration of disorder is increased. We find a scaling behavior to characterize this cross-over phenomenon. We further show how this scaling behavior is also present in another class of problems, namely two dimensional vesicles subjected to a pressure differential.     

Navigation Strategies of Motor Proteins on Decorated Tracks

Motor proteins display widely different stepping patterns as they move on microtubule tracks, from the deterministic linear or helical motion performed by the protein kinesin to the uncoordinated random steps made by dynein. How these different strategies produce an efficient navigation system needed to ensure correct cellular functioning is still unclear. Here, we show by numerical simulations that deterministic and random motor steps yield different outcomes when random obstacles decorate the microtubule tracks: kinesin moves faster on clean tracks but its motion is strongly hindered on decorated tracks, while dynein is slower on clean tracks but more efficient in avoiding obstacles. Further simulations indicate that dynein’s advantage on decorated tracks is due to its ability to step backwards. Our results explain how different navigation strategies are employed by the cell to optimize motor driven cargo transport.     

Fish-AMAZBOL: a database on freshwater fishes of the Bolivian Amazon

The Bolivian part of the Amazon Basin contains a mega diverse and well-preserved fish fauna. Since the last decade, this fish fauna has received an increasing attention from scientists and the national authorities as fishes represent one of the most important sources of proteins for local human communities. However, this fish fauna still remains poorly documented. Here, we present a database for fishes from the Bolivian Amazon. To build the database, we conducted an extensive literature survey of native and non-native (exotic) fishes inhabiting all major sub-drainages of the Bolivian Amazon. The database, named Fish-AMAZBOL, contains species lists for 13 Amazonian hydrological units, covering 100% of the Bolivian Amazon and approximately 65% (722,137 km²) of the all territory. Fish-AMAZBOL includes 802 valid species, 12 of them being non-native, that have been checked for systematic reliability and consistency. To put this number in perspective, this represents around 14% of the all Neotropical ichthyofauna and around 6% of all strictly freshwater fishes inhabiting the planet. This database is currently the most comprehensive database of native and non-native fish species richness available so far for the Bolivian Amazon.     

Population Growth of the Cladoceran,Daphnia magna: A Quantitative Analysis of the Effects of Different Algal Food

In this study, we examined the effects of two phytoplankton species, Chlorella vulgaris and Stephanodiscus hantzschii, on growth of the zooplankton Daphnia magna. Our experimental approach utilized stable isotopes to determine the contribution of food algae to offspring characteristics and to the size of adult D. magna individuals. When equal amounts of food algae were provided (in terms of carbon content), the size of individuals, adult zooplankton, and their offspring increased significantly following the provision of S. hantzschii, but not after the provision of C. vulgaris or of a combination of the two species. Offspring size was unaffected when C. vulgaris or a mixture of the two algal species was delivered, whereas providing only S. hantzschii increased the production of larger-sized offspring. Stable isotope analysis revealed significant assimilation of diatom-derived materials that was important for the growth of D. magna populations. Our results confirm the applicability of stable isotope approaches for clarifying the contribution of different food algae and elucidate the importance of food quality for growth of D. magna individuals and populations. Furthermore, we expect that stable isotope analysis will help to further precisely examine the contribution of prey to predators or grazers in controlled experiments.     

Analysis of the population structure of Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) in the Palaearctic region using microsatellite markers

Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) is widely distributed throughout the Palaearctic region. The aim was to explain the current geographic distribution of the species by investigating its genetic population structure. Samples of M. pygmaeus were collected in 15 localities through its range of distribution. A sample from a commercial producer was also analyzed. A total of 367 M. pygmaeus were genotyped for nine microsatellite loci. Isolation by distance was tested by Mantel's test. The molecular structure of M. pygmaeus populations was inferred by UPGMA, AMOVA, Principal component and Bayesian analyses. The average number of alleles per locus per population was 5.5 (range: 3.1–7.8). Istanbul (Turkey) and Nimes (France) had the lowest (0.291) and the highest (0.626) expected heterozygosity (H_e), respectively. There was an increase in H_e from the Canary Islands to Nimes, and a progressive decrease thereafter. A significant negative correlation was found between allelic richness and H_e, and the distance of each population to the easternmost locality (Canary Islands). Significant linkage disequilibrium was observed in the populations from Turkey. F_ST (0.004–0.334) indicated a high population differentiation, with isolation by distance supported by a high correlation. Bayesian analyses, PCA, and UPGMA pointed to three main clusters: (1) Greece and Turkey, (2) Italy and France, and (3) southern Iberia and the Canary Islands. The recent evolutionary history of M. pygmaeus is inferred from the data as follows: (1) the reduction in the geographic distribution of the species to the Iberian, Italian, and Balkan peninsulas, and possibly southern France, during glaciations and re‐colonization of northern Europe from its southern refuges; (2) the maintenance of high diversity in Iberia and Italy (and possibly southern France) during contraction periods, and bottlenecks in the Balkans; (3) introgression of the Italian–French lineage in northern Spain, naturally or through trade.     

The effect of the calcium antagonist nimodipine upon local cerebral glucose utilization in the rat brain

The new calcium antagonist Nimodipine has been shown to have more powerful dilator action on cerebral than peripheral vessels. The effect of the drug on cerebral metabolism was studied in conscious rats using the /14C/-2-deoxyglucose quantitative autoradiographic technique. Intravenous injection of Nimodipine, 2 mcg/Kg, determined significant increases in local cerebral glucose utilization that appeared to be homogeneous in magnitude and anatomic distribution throughout the brain. This study raises the question whether Nimodipine affects brain functions by other mechanisms than an increase in cerebral blood flow.